1. Field of the Invention
The present invention relates to a position sensor for a movable body, for example, a position sensor which is useful for an optical interferometer used in an optical measurement technical field, and an optical interferometer to which the position sensor is applied.
2. Description of the Related Art
In optical interferometers which the Michelson interferometer represents, an incident light is divided into two optical paths for a transmitted light and a reflected light, which are perpendicular to each other, by using a beam splitter. Two lights reflected on each mirror disposed so as to be perpendicular to each optical path are multiplexed by a beam splitter again.
At the same time, a stage on which one mirror is mounted is moved at a constant speed and straightly. The optical path difference between the two lights reflected on the two mirrors is caused. A variety of intensity of interference fringes can be observed. The variety of intensity of interference fringes is fetched by the photo-detector as an electric signal.
The wavelength of a light can be measured more precisely by moving the movable mirror straight and a long distance.
In order to detect the limitation on a movement of the movable mirror, that is, in order to detect a position corresponding to the limitation on a movement of the stage, according to an earlier development, a pair of limit switches is disposed in a casing on one side of a line on which the stage is moved. Each position corresponding to the limitation is detected in each direction with a pair of limit switches by using one dog provided on the stage.
However, in a position sensor according to an earlier development, because of the relation between one dog and a pair of limit switches disposed at both ends of a movable range for the stage, each amount of movement of the stage in each direction, which is defined on the basis of the neutral position of the stage is small. Therefore, the movable distance of the stage cannot be sufficiently obtained.
That is, because the position of one dog provided on the stage is detected with a pair of limit switches, each amount of movement in each direction is only a distance from one dog of the stage in the neutral position to the limit switch. Therefore, it is not possible that both the movable distance of the movable mirror is obtained sufficiently, and that the casing becomes small.
In order to solve the above-described problems, an object of the present invention is to provide a position sensor in which the movable distance of a movable body can be reasonably obtained and in which a casing for containing the movable body can be sufficiently small.
Another object of the present invention is to provide an optical interferometer in which the above position sensor is provided.
That is, in accordance with one aspect of the present invention, the position sensor for the movable body, which detects a position of the movable body which moves in a reciprocal direction, comprises;
a plurality of portions to be detected, which are provided on one side surface of the movable body with respect to a moving direction of the movable body, and which are arranged in different positions from each other in a direction along the moving direction of the movable body and in a direction crossing the moving direction, and
a plurality of detectors which are arranged so that each detector corresponds to each portion to be detected.
As a movable body, a movable mirror for an optical interferometer, which moves straightly is used. However, the present invention is not limited to this. The movable body may be one which moves along a curved line.
As a portion to be detected, a dog which projects from the movable body is used. However, the present invention is not limited to this. Any portion to be detected may be used.
As a detector, a photoelectric type of detector is used. However, the detector may be a magnetic type of detector, an electronic type of detector or a mechanical type of detector.
According to the present invention, the position sensor comprises a plurality of portions to be detected. The plurality of portions to be detected are provided on one side surface of the movable body. The plurality of portions to be detected move in a reciprocal direction, with respect to a moving direction of the movable body. The plurality of portions to be detected are arranged in different positions from each other in a direction along the moving direction of the movable body and in a direction crossing the moving direction. The position sensor further comprises a plurality of detectors which are arranged so that each detector corresponds to each portion to be detected. The movable body can be moved a long distance, for example, from each portion to be detected, of the movable body in a neutral position to each corresponding detector. The amount of movement of the movable body can be detected, by detecting the plurality of portions to be detected. The plurality of portions to be detected are provided on one side surface of the movable body in different positions from each other in a direction along the moving direction and in a direction crossing the moving direction, with the corresponding detectors.
Therefore, the movable distance of the movable body can be obtained reasonably. Because a plurality of portions to be detected and a plurality of detectors are arranged on one side of the movable body with respect to the moving direction of the movable body, a casing for containing the movable body can be small.
The plurality of portions to be detected may be a pair of dogs projecting from the movable body, and the plurality of detectors may be a pair of photoelectric type of detectors.
According to the present invention, because the portions to be detected are a pair of dogs projecting from the movable body and the detectors are a pair of photoelectric type of detectors, the amount of movement of the movable body in a reciprocal direction can be detected by a photoelectric sensing method in which the dogs are not in contact with the detectors.
In accordance with another aspect of the present invention, the optical interferometer in which a reference light and a light to be measured interfere with each other by a plurality of optical parts, is one wherein the plurality of optical parts are separated into a fixed optical part and a movable optical part. The fixed optical part is fixed to a casing and a movable optical part is movable with respect to the casing. The optical interferometer comprises a position sensor for the movable optical part, which detects a position of a movable optical part which moves in a reciprocal direction.
The optical interferometer further comprises a plurality of portions to be detected, which are provided on one side surface of the movable optical part with respect to a moving direction of the movable optical part. The plurality of portions to be detected are arranged in different positions from each other in a direction along the moving direction of the movable optical part and in a direction crossing the moving direction. The optical interferometer further comprises a plurality of detectors which are arranged so that each detector corresponds to each portion to be detected. For example, as an optical part, a beam splitter or a reflector is used.
According to the present invention, because the movable optical part is disposed on an optical axis which is approximately parallel to an optical axis of the reference light, the wavelength of a light can be measured more precisely by moving the movable optical part a long distance along an optical axis which is approximately parallel to the optical axis of the reference light. Further, the casing can be sufficiently small.
Because the position of the movable optical part is detected by using the above position sensor, the movable distance of the movable optical part can be obtained reasonably. The casing can be small.
In accordance with another aspect of the present invention, the optical interferometer has a reference light and a light to be measured. The reference light and light to be measured branch into two optical paths for a transmitted light and a reflected light, which are perpendicular to each other, by a beam splitter. After the reflected light and the transmitted light are reflected on a plurality of reflecting members each other in each optical path, the reflected light and the transmitted light are multiplexed by the beam splitter to receive the multiplexed light by a photo-detector. The optical interferometer has the plurality of reflecting members which are separated into a fixed reflecting member which is fixed to a casing and a movable reflecting member which is movable with respect to the casing.
The optical interferometer comprises a position sensor for the movable reflecting member, which detects a position of a movable reflecting member which moves in a reciprocal direction. The position sensor has a plurality of portions to be detected, which are provided on one side surface of the movable reflecting member with respect to a moving direction of the movable reflecting member, and which are arranged in different positions from each other in a direction along the moving direction of the movable reflecting member and in a direction crossing the moving direction. The position sensor further has a plurality of detectors which are arranged so that each detector corresponds to each portion to be detected.
For example, a representative reflecting member is a mirror. Instead of a mirror, for example, a corner cube or a reflector may be used.
The photo-detector is one for fetching a variety of intensity of interference fringes as an electric signal.
According to the present invention, because the movable reflecting member is disposed on an optical axis which is approximately parallel to an optical axis of the reference light, the wavelength of a light can be measured more precisely by moving the movable reflecting member a long distance along an optical axis which is approximately parallel to the optical axis of the reference light. Further, the casing can be sufficiently small.
Because the position of the movable reflecting member is detected by using the above position sensor, the movable distance of the movable reflecting member can be obtained reasonably. The casing can be small.
A pair of fixed reflecting members for reflecting the reflected light and the transmitted light toward the other fixed reflecting member each other may be provided, and a pair of movable reflecting members for totally reflecting a light toward each fixed reflecting member may be disposed between the pair of fixed reflecting members.
According to the present invention, because a pair of movable reflecting members for totally reflecting a light toward each fixed reflecting member is disposed between the pair of fixed reflecting members for reflecting the reflected light and the transmitted light toward the other fixed reflecting member each other, a wide range in which an optical path difference between two lights is caused can be obtained by moving the pair of movable reflecting members between the pair of fixed reflecting members on an optical axis which is approximately parallel to the optical axis of the reference light so as to reflect each light totally.
In accordance with another aspect of the present invention, the position sensor for movable body, which detects a position of a movable body which moves in a reciprocal direction, comprises at least two portions to be detected and at least two detectors for detecting the portions to be detected. The at least two portions to be detected, which are provided on one side surface of the movable body with respect to a moving direction of the movable body. The at least two detectors for detecting the portions to be detected comprise one portion to be detected that is not arranged on a line parallel to the moving direction, on which the other portion is disposed, nor arranged on a line perpendicular to the moving direction, on which the other portion is disposed. The at least two detectors for detecting the portions to be detected further comprise one detector corresponding to the one portion that is arranged so that when the one detector detects the one portion by moving the movable body in one direction, the other portion is moved in the one direction beyond the one detector. The at least two detectors further comprise an other detector corresponding to the other portion that is arranged so that when the other detector detects the other portion by moving the movable body in the other direction, the one portion is moved in the other direction beyond the other detector.